Continuing the research on control mechanisms in immune function has demonstrated that spleen cells from old mice produce more interferon than do cells from young mice, but the cells from the old mice are less affected by the interferon because of a relative lack of membrane interferon receptors. Therefore interferon and interferon inducing agents have a greater effect on the cells from young mice. Also, the metal Zinc has been shown to be able to boost in vitro antibody responses of spleen cells from old mice. Along with other evidence that Zinc is important in the activation of thymic hormone from an inactive to the active state it may be that in vivo administration of Zinc to old mice or humans could improve immune function.